It is a well known characteristic of stannous octoate, when used as a catalyst in room temperature vulcanizing silicone compositions, to find that it loses all of its catalytic activity upon repeated opening and closing of the containers in which it is stored, alone or as commonly diluted for use in a silicone fluid, e.g., a trimethylsilyl-stopped dimethyl polysiloxane. The loss in activity is apparently due primarily to oxidation of stannous tin to the inactive stannic tin by air or by air and moisture during exposure. Somewhat better results are obtained if stannous octoate is replaced by stannous salts of branch chain carboxylic acids having from 8 to 12 carbon atoms. Best results in this series are obtained if the acids are fully branched. Stannous neodecanoate, which has 10 fully branched carbon atoms, is especially improved in stability in comparison to stannous octoate. However, when these more stable stannous salts are diluted in a dimethyl polysiloxane fluid to facilitate storage, measurement and compounding these are found to deteriorate quickly on air exposure.
It has now been discovered that if the stannous salts of branched chain alkyl carboxylic acids having from 8 to 12 carbon atoms are combined with a very specific type of organopolysiloxane carrier fluid, there will be obtained a very superior catalyst composition. In particular, a stable, active catalyst composition is obtained using as carrier fluid, a methyl alkyl polysiloxane having hydroxy aryl substituents. These fluids appear to solubilize the stannous salts of branched carboxylic acids very readily and, at the same time, provide in solubilized form a hindered phenolic type substituent which effectively retards the oxidation of stannous tin to inactive stannic tin. Somwhat surprisingly, this same fluid does not readily solubilize the conventional tin soap catalyst, stannous octoate, and many attempts to provide catalysts system based on this fluid and stannous octoate have failed because such compositions deteriorate rapidly upon air exposure.
Such novel catalyst compositions are superior to conventional stannous soap compositions in all room temperature vulcanizing rubber formulations, but they are vastly superior to stannous octoate compositions in the production of articles having silicon compositions injected and then cured in place, in contact with human body parts. Such articles comprise footwear, such as shoes, boots and the like, custom-fitted to the foot of the wearer, and they are disclosed and claimed in the copending application of Robert L. Blomquist, Alfred H. Smith, Jr., Robert A. Smith and Richard P. Surprenant, entitled, FOOTWEAR INCLUDING CORE OF CUSTOM FITTING COMPOSITION, filed in the United States Patent Office on Dec. 5, 1973, Ser. No. 421,968, now abandoned, assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. The present invention has, as one of its principal features, the provision of a curable, injectable syntactic foam composition for custom fitting footwear, catalyzed with the new stabilized composition.